U.S. diplomats concluded in late 2008 that the government of Armenia had supplied Iran with rockets and machine guns later used to kill American troops in Iraq, according to State Department cables disclosed by WikiLeaks.

John D. Negroponte, deputy secretary of state at the time, wrote a December 2008 letter to Armenian President Serzh Sargsyan expressing “deep concerns about Armenia’s transfer of arms to Iran which resulted in the death and injury of U.S. soldiers in Iraq.”

The cable, based on U.S. intelligence, includes the text of a classified letter labeled “secret” from Mr. Negroponte. It says “in 2007 some of these weapons were recovered from two Shia militant attacks in which a U.S. soldier was killed and six others were injured in Iraq.”

The disclosure of the re-export of arms by Armenia is one example of how the leaked archive of U.S. diplomatic traffic totaling more than 250,000 reports reveals an extensive U.S. government effort to stop allies and adversaries alike from arming Iran with even conventional weapons.

In Tehran, President Mahmoud Ahmadinejad said Monday that the documents made public by WikiLeaks is part of a campaign by the CIA and the Israeli Mossad. While many cables showed heads of Arab states urging the United States to take military action against Iran, Mr. Ahmadinejad dismissed them as propaganda. “The countries in the region are like friends and brothers,” he said. “These acts of mischief will not affect their relations.”

Secretary of State Hillary Rodham Clinton said in Washington that the leaks will not affect U.S. relationships with allies. Yet she also said that the disclosures would endanger people in closed societies who had spoken with U.S. diplomats.

“There is nothing laudable about endangering innocent people, and there is nothing brave about sabotaging peaceful relations between nations on which our common security depends,” Mrs. Clinton said.

Mrs. Clinton said WikiLeaks acted illegally in posting the classified document and that the Obama administration is taking “aggressive steps to hold responsible those who stole this information.”

At the Justice Department, Attorney General Eric H. Holder Jr. said the government had launched a criminal probe, while Pentagon officials said security is being tightened to better control digital storage devices such as CDs and flash drives.

The Armenian incident was part of a wider U.S. effort to block Iran’s access to the global arms and weapons technology market. For example, a 2010 cable revealed covert U.S. efforts to persuade China’s government to block a sale from a Malaysian firm, Electronics Component Ltd., to sell gyroscopes to an Iranian front company.

The cables also show U.S. diplomatic efforts to stop German sales of high-technology equipment to Iranian front companies and block conventional arms sales from Turkey to Iran. Both countries are NATO allies.

In some cases though, the cables show the inefficacy of the American effort. North Korea, according to one cable in 2007, successfully shipped missile components to Iran despite U.S. efforts to seek Chinese help in blocking the transfer.

“This shows the breadth of the U.S. effort to quietly shut down all the various spigots and channels that the United States was using to bleed the United States in Iraq and Afghanistan,” said Kenneth Katzman, an Iran specialist at the Congressional Research Service. “We have seen a recent example in Nigeria of arms pipelines being exposed, these cables show more of a sweep to it than most Americans were aware of, which is usually limited to public discussion of U.N. sanctions votes.”

Mr. Katzman said the worldwide U.S. effort reminded him of Operation Staunch in the 1980s. “It hearkens back to U.S. efforts during the Iran-Iraq war to prevent conventional arms deliveries to Iran, which had a degree of success but was not a complete hermetic seal,” he said.

The disclosures about Armenian government links to Iran arms supplies are surprising. Armenia has drawn closer to the United States in recent years as the United States has sought to quietly broker Armenia’s disputes with Turkey and Azerbaijan.